RE: Rebuild Indexes

DENNIS WILLIAMS

2004-02-17

Juan In the Dec 2001 edition of the Student Guide, that statement appears onpage 14-12. I think the paragraph preceding the one you quoted sets thecontext for the statement a bit:

How to Solve B-Tree Index Performance Degradation

The more levels an index has, the less efficient it may be. Additionally, anindex with many rows deleted might not be efficient. Typically, if 15% ofthe index data is deleted, then you should consider rebuilding the index.

You should rebuild your indexes regularly. However, this can be atime-consuming task, especially if the base table is very large . . . theparagraph then goes on to describe the index rebuilding options.

Juan - If you search the archive for this list, you will find where thetopic of rebuilding indexes has been discussed many times. This should giveyou some more background on the issue. Second, while the Student Guides aregreat for helping pass the OCP, they are primarily oriented toward peoplenew to Oracle. As you become more experienced in Oracle, you should digdeeper, particularly on vague topics like "when to rebuild indexes". Third,while the sentence in the Student Guide does say "rebuild your indexesregularly", the context of the statement is really discussing all thewonderful new Oracle9i features that make rebuilding indexes a less oneroustask.

I couldn't actually find your quote in the Performance Tuning Guide for 8.1=.7, 9.2 or 10.1. Is it perhaps some other book?=20

Niall LitchfieldOracle DBAAudit Commission+44 117 975 7805=20

> -----Original Message-----> From: j.miranda@(protected)> Sent: 17 February 2004 10:41> To: j.miranda@(protected)> Subject: RE: Rebuild Indexes>=20>=20>=20> Hi>=20> May script do just original post (vidya kalyanaraman) as for.> No more.=20>=20> May be is not adecuate for your system.=20> Anyway you can stop it when you want: a simple CTRL+C.>=20> In my mail I say:=20> "Take care in production because VALIDATE STRUCTURE do some=20> tipe of lock.">=20> I have a very busy database and I execute this script very=20> care and control.> I do it once a year and this reduced to 1/3 the space ocupied=20> by indexes.>=20> I will no discuss if it is good or not to rebuild indexes but...> Oracle Performance Tuning Manual 12-12:> "You sould rebuild your indexes regularly. However, this can be a> time-consuming task, especially if the base table es very large.">=20> Sorry if it caused problems in your system but ask Oracle for a better> rebuild method, not me.>=20> I forgot to add an "alter session set SORT_AREA_SIZE=3D25000000;". This= > do it faster.>=20> Grettings.>=20>=20> -----Mensaje original-----> De: oracle-l-bounce@(protected)> [mailto:oracle-l-bounce@(protected)> nombre de Richard Foote> Enviado el: viernes, 13 de febrero de 2004 14:59> Para: oracle-l@(protected)> Asunto: Re: Rebuild Indexes>=20> When to rebuild indexes, hummm, this is all rather new and exciting ;)>=20> Juan, I notice with interest that your script:>=20> - performs an analyze validate structure on all indexes> - rebuilds all indexes if guilty of having more than 2 levels> - rebuilds all indexes with more than 10% deleted rows>=20> Running such a script on our production databases at my=20> current site would:>=20> - cripple performance for up to approximately 14 hours=20> (depending on> database) performing just the analyze step> - rebuild every single one of our larger, 3+ level=20> indexes (don't want> to think about the cost of this)>=20> for practically *no* benefit.>=20> The 3+ criteria does "accidentally" rebuild the handful we've=20> identified as> being candidates for an occasional rebuild but boy, what an=20> incredible price> to pay !!>=20> I think not ...>=20> Richard Foote>=20> ----- Original Message -----> From: "Juan Miranda" <j.miranda@(protected)>> To: <oracle-l@(protected)>> Sent: Friday, February 13, 2004 7:14 PM> Subject: RE: Rebuild Indexes>=20>=20>=20> Hi>=20> Try this.> This do not use a cursor so you can stop it when you what.> Take care in production because VALIDATE STRUCTURE do some=20> tipe of lock.>=20>=20> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++> +++++++++++=3D> +++> -- Juan Miranda Serm=3DE1tica 06/AGO/2002> -- Utiliza VALIDATE STRUCTURE -> OJO en producci=3DF3n. Puede generar =3D> errores> ORA-00054.> -- OJO nolog -> NO usar con stand by>=20>=20> set serveroutput on size 1000000> set pagesize 0> set feedback off> set echo off> set trimspool on>=20> spool c:\reb_index1.sql>=20> DECLARE> dbname varchar2(20);> wday varchar2(11);> BEGIN> dbms_output.put_line('set echo off');> dbms_output.put_line('set feedback off');> dbms_output.put_line('set head off');>=20> dbms_output.put_line('spool c:\reb_index2.sql');> dbms_output.put_line('prompt set feedback on');> dbms_output.put_line('prompt set echo on');> dbms_output.put_line('prompt spool c:\reb_index2.log');>=20> FOR t IN (select owner, index_name from dba_indexes where=20> owner not =3D> in> ('SYS','SYSTEM') order by owner,index_name) LOOP>=20> dbms_output.put_line('prompt --Analizando> '||t.owner||'.'||t.index_name);>=20> dbms_output.put_line('Analyze index=20> '||t.owner||'.'||t.index_name||'> validate structure;');>=20> dbms_output.put_line('select ' || '''' || 'Alter index '=20> || t.owner =3D> ||> '.' || t.index_name || ' rebuild online;' || ''''|| ' from=20> index_stats =3D> where> (height > 2) or> (10<=3D3Ddecode(lf_rows_len,0,NULL,((del_lf_rows_len/lf_rows_len> )*100)));')=3D> ;>=20> END LOOP;>=20> dbms_output.put_line('prompt spool off');> dbms_output.put_line('spool off');> dbms_output.put_line('@(protected)');>=20> END;> /> spool off>=20> @c:\reb_index1.sql>=20> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++> +++++++++++=3D> +++>=20>=20>=20>=20> -----Mensaje original-----> De: oracle-l-bounce@(protected)> [mailto:oracle-l-bounce@(protected)> En> nombre de vidya kalyanaraman> Enviado el: viernes, 13 de febrero de 2004 9:46> Para: oracle-l@(protected)> Asunto: Rebuild Indexes=3D20>=20> Hi> It may be a silly thing to ask, but I am stuck right now.=3D20> I have been given a task to find out the indexes which need to be=3D20> rebuilt. There are around 3000 Indexes. I know I can run=20> the following =3D>=20> command> "analyze index <Index> VALIDATE STRUCTURE " =3D20>=20> for a single index and then find the rows from index_state=20> based on=3D20> del_lf_rows_len/lf_rows_len > 20%. =3D20> Does anyone have a script for dynamically finding out the=20> indexes that=3D20> are the candidates for rebuilding? How do you normally handle=3D20> situations like this?>=20> TIA> Vidya>=20>=20>=20>=20>=20> ----------------------------------------------------------------> Please see the official ORACLE-L FAQ: http://www.orafaq.com> ----------------------------------------------------------------> To unsubscribe send email to: oracle-l-request@(protected)> put 'unsubscribe' in the subject line.> --> Archives are at http://www.freelists.org/archives/oracle-l/> FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html> ----------------------------------------------------------------->=20> ----------------------------------------------------------------> Please see the official ORACLE-L FAQ: http://www.orafaq.com> ----------------------------------------------------------------> To unsubscribe send email to: oracle-l-request@(protected)> put 'unsubscribe' in the subject line.> --> Archives are at http://www.freelists.org/archives/oracle-l/> FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html> ----------------------------------------------------------------->=20>=20>=20> ----------------------------------------------------------------> Please see the official ORACLE-L FAQ: http://www.orafaq.com> ----------------------------------------------------------------> To unsubscribe send email to: oracle-l-request@(protected)> put 'unsubscribe' in the subject line.> --> Archives are at http://www.freelists.org/archives/oracle-l/> FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html> ----------------------------------------------------------------->=20> ----------------------------------------------------------------> Please see the official ORACLE-L FAQ: http://www.orafaq.com> ----------------------------------------------------------------> To unsubscribe send email to: oracle-l-request@(protected)> put 'unsubscribe' in the subject line.> --> Archives are at http://www.freelists.org/archives/oracle-l/> FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html> ----------------------------------------------------------------->=20>=20

**********************************************************************This email contains information intended forthe addressee only. It may be confidentialand may be the subject of legal and/orprofessional privilege. Any dissemination,distribution, copyright or use of thiscommunication without prior permission ofthe sender is strictly prohibited.**********************************************************************

----------------------------------------------------------------Please see the official ORACLE-L FAQ: http://www.orafaq.com----------------------------------------------------------------To unsubscribe send email to: oracle-l-request@(protected)put 'unsubscribe' in the subject line.--Archives are at http://www.freelists.org/archives/oracle-l/FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html-----------------------------------------------------------------

----------------------------------------------------------------Please see the official ORACLE-L FAQ: http://www.orafaq.com----------------------------------------------------------------To unsubscribe send email to: oracle-l-request@(protected)put 'unsubscribe' in the subject line.--Archives are at http://www.freelists.org/archives/oracle-l/FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html---------------------------------------------------------------------------------------------------------------------------------Please see the official ORACLE-L FAQ: http://www.orafaq.com----------------------------------------------------------------To unsubscribe send email to: oracle-l-request@(protected)put 'unsubscribe' in the subject line.--Archives are at http://www.freelists.org/archives/oracle-l/FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html-----------------------------------------------------------------